Two of the more relevant trends in the optical networking area are the increase in network capacity and the increase in transmission reach. A higher network capacity is obtained by increasing the channel rate, e.g., with TDM (time division multiplexing), and/or by increasing the channel density, e.g., with WDM (wavelength division multiplexing).
Advances in transmitter and receiver design, evolution of optical amplification, employment of distributed Raman amplification combined with various dispersion compensation techniques, new encoding and modulation techniques, digital wrapper technology, etc., have enabled the installation of ultra-long reach networks, where regeneration of the signal is effected at 3,000 km or more.
However, current WDM networks use point-to-point connectivity, which means that all channels are OEO (optical-to-electrical-to-optical) converted at each node. In addition, the point-to-point network requires duplication of equipment for protection/restoration in case of faults. As a result, the configuration of a typical node of a point-to-point network is very complex. On the other hand, OEO conversion at all intermediate nodes is not necessary in the majority of cases, since the modern ultra-long reach (ULR) techniques allow optical signals to travel distances greater than the distance between two or more successive nodes without regeneration. Thus, important cost savings may be obtained by eliminating the unnecessary OEO conversion equipment.
There is a need to reduce the cost of the network nodes by maximizing the distance traveled by the signals in optical format, to take advantage of the emerging ULR techniques and to provide a more efficient use of the network equipment. Furthermore, scaling-up and/or providing new services in a point-to-point network requires very complex network engineering and planning involving extensive simulation and testing. Moreover, the waiting time for a new optical service in point-point networks can be over 120 days.
There is a need to break the wavelength engineering bottleneck currently constraining the engineering-to-provisioning ratio, and for wavelengths to become available as a network resource automatically deployable across the network. There is also a need to minimize the number of wavelengths that are deployed while avoiding the color clash effect for optical signals having different wavelengths and sharing a single fiber, for efficient use of all network resources.
Automatic switching and regeneration functionality results in regenerators and wavelengths becoming two of the most important resources of the photonic networks. In general, they could be allocated to a connection according to certain rules, which are mostly dictated by the class of service for the respective connection and by the particular architecture of the network. Methods to economically use these resources and minimize blocking of new connection requests are crucial to cost reduction and operational efficiency of photonic networks.
Determination of the number of regenerators and their nodal allocations is one aspect of efficient resource management in photonic networks. Regenerators need to be switched into an end-to-end connection so that the signal is regenerated and restored to superior quality before propagation and transmission impairments corrupt the signal entirely. Nodal allocation of regenerators is performed with a view to optimize the network cost, and depends mainly on maintaining a current view of the nodal configuration, including regenerator availability and type.
Further, in switched optical networks, the selection and assignment of the correct wavelength to each optical path for the best possible utilization of available wavelengths depends on several factors. These factors can include: (a) maintaining a current view of the current network connectivity; and (b) since “not all wavelengths are equal”, providing the network with the knowledge of the individual wavelength performance. Knowing the current wavelength allocation allows the network to select one or more unused wavelengths to serve a new connection. This is even more important having in view that this allocation is dynamic, the connections being set-up and removed by users at arbitrary moments. Knowing the individual performance of all wavelengths available in the network and the pertinent topology information (e.g., fiber type, link loading, etc), allows matching a wavelength to an optical path, which allows further reduction of the network costs.
Nonetheless, selection and assignment of the correct wavelength for each optical path for the best possible utilization of available wavelengths is a complex problem. A meaningful solution to this complex problem is needed to facilitate the best possible use of wavelengths as a resource while satisfying connection setup demands.